Paper structures, such as toilet tissue, paper towels, and facial tissue, are widely used throughout the home and industry. Many attempts have been made to make such tissue products more consumer preferred. One approach to providing consumer preferred tissue products having bulk and flexibility is illustrated in U.S. Pat. No. 3,994,771 issued Nov. 30, 1976 to Morgan et al. Improved bulk and flexibility may also be provided through bilaterally staggered compressed and uncompressed zones, as shown in U.S. Pat. No. 4,191,609 issued Mar. 4, 1980 to Trokhan.
Another approach to making tissue products more consumer preferred is to dry the paper structure to impart greater bulk, tensile strength, and burst strength to the tissue products. Examples of paper structures made in this manner are illustrated in U.S. Pat. No. 4,637,859 issued Jan. 20, 1987 to Trokhan. Alternatively, a paper structure can be made stronger, without utilizing more cellulosic fibers, by having regions of differing basis weights as illustrated in U.S. Pat. No. 4,514,345 issued Apr. 30, 1985.
Tissue paper manufacturers have also attempted to make tissue products more appealing to consumers by improving the aesthetic appearance of the product. For example, embossed patterns formed in tissue paper products after the tissue paper products have been dried are common. One embossed pattern which appears in cellulosic paper towel products marketed by the Procter and Gamble Company is illustrated in U.S. Pat. No. Des. 239,137 issued Mar. 9, 1976 to Appleman. Embossing is also illustrated in U.S. Pat. No. 3,556,907 issued Jan. 19, 1971 to Nystrand; U.S. Pat. No. 3,867,225 issued Feb. 18, 1975 to Nystrand; and U.S. Pat. No. 3,414,459 issued Dec. 3, 1968 to Wells.
However, embossing processes typically impart a particular aesthetic appearance to the paper structure at the expense of other properties of the structure. In particular, embossing a dried paper web disrupts bonds between fibers in the cellulosic structure. This disruption occurs because the bonds are formed and set upon drying of the embryonic fibrous slurry. After drying the paper structure, moving fibers normal to the plane of the paper structure by embossing breaks fiber to fiber bonds. Breaking bonds results in reduced tensile strength of the dried paper web. In addition, embossing is typically done after creping of the dried paper web from the drying drum Embossing after creping can disrupt the creping pattern imparted to the web. For instance, embossing can eliminate the creping pattern in some portions of the web by compacting or stretching the creping pattern. Such a result is undesirable because the creping pattern improves the softness and flexibility of the dried web.
In addition, dry embossing a paper structure acts to stretch or draw the paper structure around the perimeter of the embossments. As a result, the paper structure around the perimeter of the embossments will have a reduced thickness relative to the non-embossed portion of the paper web.
Felts for use in papermaking are also well known. U.S. Pat. No. 3,537,954 issued to Justus discloses imparting a creping pattern to a web with a felt having yarns running in the cross machine direction along the outer surface of the felt. U.S. Pat. No. 4,309,246 issued to Hulit et al. discloses pressing a web between a felt and an imprinting fabric. U.S. Pat. No. 4,144,124 issued to Turunen et al. discloses a paper machine having a twin-wire former having a pair of endless fabrics, which can be felts. One of the endless fabrics carries a paper web to a press section. The press section can include the endless fabric which carries the paper web to the press section, an additional endless fabric, and a wire for patterning the web. U.S. patent application Ser. No. 08/170,140, Method of Pressing and Molding a Paper Sheet, filed Dec. 20, 1993 in the name of Ampulski et al. discloses a process for molding and dewatering a paper web which employs dewatering felts.
U.S. Pat. No. 4,446,187 to Eklund discloses a sheet assembly which can be used as a forming fabric, press fabric, and drying fabric porous belt, including as a press felt and a drying felt. The sheet assembly includes a foil and a reinforcement structure bonded together. The foil can be formed from a plastic material, and is formed with through-holes. Eklund teaches that it is desirable to produce a belt fabric which possesses as even a surface as possible to provide an even pressure distribution and to avoid a coarse surface structure in the finished paper. Eklund teaches that by adapting the diameter and positions of the holes in the foil, it is possible to obtain a dewatering belt possessing a very even pressure distribution.
U.S. Pat. No. 4,740,409 to Lefkowitz discloses a nonwoven fabric having parallel machine direction yarns and interconnecting cross machine direction polymeric material surrounding the machine direction yarns. The cross machine direction polymeric material contains spaced perforations through the fabric.
PCT Publication Number WO 92/17643 published Oct. 15, 1992 in the name of Buchanan et al. and assigned to the SCAPA Group discloses a base fabric for use in producing a papermakers fabric. The base fabric includes superimposed layers of thermoplastic materials in mesh form. Buchanan teaches that the base fabric can be embodied in a marking felt.
PCT Publication Number WO 91/14558 published Oct. 3, 1991 in the name of Sayers et al. and assigned to the SCAPA Group discloses a method of making an apertured polymeric resin material use in papermaking by curing a radiation curable polymeric material. Sayers et al. teaches that the apertured structure may be combined with a textile bait to form a papermakers dewatering felt. U.S. Pat. No. 4,514,345 issued Apr. 30, 1985 to Johnson et al. teaches a method of making a foraminous member with a photosensitive resin.
U.S. patent application Ser. No. 07/718,452 now abandoned, with continuation application Nos. 08/033713 and 08/189,242 now issued U.S. Pat. Nos. 5,328,565 and 5,431,786. Tissue Paper Having Large Scale, Aesthetically Discernible Patterns and Apparatus for Making Same, filed Jun. 19, 1991 in the name of Rasch et al. discloses a single lamina paper structure having at least three visually discernible regions. Rasch et al. teaches the three regions are visually distinguishable by an optically intensive property such as crepe frequency, elevation, or opacity. Rasch et al. teaches that opacity can be increased by increasing the density of a region. Rasch et al. also teaches that differences in elevation between adjacent regions can be imparted to a paper structure by differences in elevation of the distal ends of adjacent flow elements. While the structures of Rasch et al. provide an improvement over embossed paper structures, there is a need to provide tissue products having improved visually discernible patterns over those taught in Rasch et al. Therefore, those involved in the papermaking field continue to search for ways to make paper structures having highly discernible aesthetic patterns without sacrificing desirable paper web properties.
Accordingly, one object of the present invention is to provide a paper structure having visually discernible patterns without the need for embossing a dried paper web.
Another object is to provide a paper structure having visually discernible patterns without sacrificing desirable paper web properties such as tensile strength and sheet flexibility.
Another object is to provide a paper structure having an enhanced bulk caliper.
Another object is to provide a paper structure having a transition region interconnecting first and second regions disposed at different elevations, wherein the transition region thickness is greater than the thickness of the second region, and greater than or equal to the thickness of tile first region.
Another object is to provide a paper structure having first and second regions disposed at different elevations, wherein the first and second regions are foreshortened, such as by creping
Another object is to provide an apparatus and process for making such a paper structure.
Another object of the present invention is to provide a web patterning apparatus comprising a dewatering felt layer and a web patterning layer comprising a photosensitive resin which penetrates a surface of tile felt layer.
Another object of the present invention is to provide a method for casting a web patterning layer of photosensitive resin onto the surface of a dewatering felt layer.